Process of preparing polyethylene terephthalate resin using a group iv-a,v-a,or viii metal salt of orthoarsenious acid or orthoarsenic acid as polycondensation catalyst



United States Patent US. Cl. 260-75 7 Claims ABSTRACT OF THE DISCLOSUREProcess of preparing polyethylene terephthalate resin comprisingcarrying out an ester-interchange reaction between ethylene glycol anddimethyl terephthalate or carrying out a direct esterification reactionbetween ethylene glycol and terephthalate acid and polycondensing thereaction product thereof in the presence of a heavy metal salt oforthoarsenious acid or orthoarsenic acid wherein the metal component ofthe salt is from Groups IV-A, V-A, or VIII of the Periodic Table.

This invention relates to an improved method for the preparation oflinear polyesters. More particularly, it relates to an improvedpolycondensation catalyst for use in the manufacture of highly polymericlinear polyesters.

It is known that linear polyesters can be prepared from a suitable esterof a dicarboxylic acid or a dicarboxylic acid by initially reacting sucha material with a diol. When an ester of a dicarboxylic acid is used asa starting material, it is first reacted with a diol in the presence ofa transesterification catalyst by means of an ester-interchangereaction; whereas, when a dicarboxylic acid is used as a startingmaterial, it is first subjected to a direct esterification reaction witha diol in the presence of what is generally called a first stagecatalytic additive or ether inhibitor. In either instance, the resultingreaction product, which may be, in general, described as a polyesterprepolymer, is then polycondensed in the presence of a polycondensationcatalyst to form a polyester resin.

In the case of the transesterification method of preparing polyethyleneterephthalate wherein ethylene glycol is reacted with dimethylterephthalate, the first stage product of the transesterificationreaction is generally described as being comprised mainly ofbis-2-hydroxyethyl terephthalate. Whereas, the first stage reactionproduct of the direct esterification reaction between ethylene glycoland terephthalate acid is comprised of bis-Z-hydroxyethyl terephthalatealong with substantial quantities of higher condensates of ethyleneglycol and terephthalic acid. In particular, the product of the directesterification reaction between ethylene glycol and terephthalic acidand the product of the transesterification reaction between dimethylterephthalate and ethylene glycol can be described as bis-Z-hydroxyethylterephthalate or a polycondensation product thereof, wherein the DP.(degree of polymerization) varies from about 2 to about 6. However, forpurposes of simplicity in describing the present invention, hereinafterthe terms polyester prepolymer and bis- 2-hydroxyethyl terephthalatewill both denote and include within their scope the product of thedirect esterification reaction between terephthalic acid and ethyleneglycol and the product of the transesterification reaction betweendimethyl terephthalate and ethylene glycol as set forth above.

Heretofore, various materials have been suggested as polycondensationcatalysts for polycondensing the polyester prepolymer products of boththe transesterification method and direct esterification method ofpreparing polyester resins. However, in general, none of the substancesthat have been suggested as polycondensation catalysts heretofore havebeen completely satisfactory. For example, many of the polycondensationcatalysts of the prior art only catalyze the condensation reaction to alow degree and they do not promote the reaction rate sufficiently to beacceptable for commercial purposes. Therefore, such polycondensationcatalysts o fthe prior art do not act to form polyester products havingcarboxyl contents as low as required for some resin uses, or molecularWeights and melting points as high as desired.

From a commercial standpoint, it is essential that a polyester resin beproduced in the shortest possible time and the desired degree ofpolymerization be obtained. A polyethylene terephthalate resin suitablefor melt spinning should have a carboxyl content value of about or belowequivalents per million grams (eq./10 gr. or meq./kg.), a melting pointof preferably at least about 258260 C., and an intrinsic viscositypreferably not less than about 0.60 (determined in a phenol and 40%tetrachloroethane solution, wt./wt., at 30 C.), in order for thefilaments formed therefrom to possess a satisfactory level of hydrolyticstability, thermal stability, ultra-violet light stability and a highdegree of tenacity which is necessary for use of such filaments in themanufacture of fibers such as are used in Wash and wear clothing.

It is an object of the present invention to prepare highly polymericlinear polyesters by a direct esterification reaction between adicarboxylic acid and a diol or by a transesterification reactionbetween an ester of a dicarboxylic acid and a diol, so as to form apolyester prepolymer and the polycondensation of the said polyesterprepolymer in the presence of an improved polycondensation catalyst.

It is another object of the present invention to prepare a highlypolymeric linear polyester resin by polycondensing bis-Z-hydroxyethylterephthalate in the presence of an improved polycondensation catalyst.

These and other objects are accomplished in accordance with the presentinvention which involves a method for preparing highly polymeric linearpolyesters wherein dimethyl terephthalate is reacted with ethyleneglycol in the presence of an ester-interchange catalyst to form apolyester prepolymer or where terephthalic acid is reacted with ethyleneglycol in the presence of a first stage catalytic additive to form apolyester prepolymer and where the resulting polyester prepolymer ispolycondensed in the presence of a polycondensation catalyst, theimprovement comprising carrying out the polycondensation of thepolyester prepolymer in the presence of a catalytic amount of a suitableheavy metal salt of orthoarsenious acid or orthoarsenic acid, which mayalso be called orthoarsenites or orthoarsenates of heavy metals.

The heavy metal orthoarsenites and orthoarsenates that can be used aspolycondensation catalysts in the present method may be suitably variedto meet any requirements of reaction conditions and desired product.While the present invention is not to be limited to any particularsuitable orthoarsenites and orthoarsenates, it has been found that thepreferred heavy metal orthoarsenites and orthoarsenates are thosewherein the metal component is from Groups IIB, IV-A, V-A, and VIII ofthe Periodic Table (see Merck Index, sixth edition, inside front cover).For example, among the polycondensation catalysts that can be used inaccordance with the present invention are antimony orthoarsenite,antimony orthoarsenate, lead orthoarsenate, tin orthoarsenate, cobaltorthoarsenate, and zinc orthoarsenate or any combination thereof.

The preparation of polyesters via the ester-interchange reaction isgenerally carried out with a molar ratio of glycol, such as ethyleneglycol, to a dialkyl terephthalate, such as dimethyl terephthalate, offrom about 1: 1 to about 15: 1, respectively, but preferably from about1.2:1 to about 2.6: 1. The transesterification reaction is generallycarried out at atmospheric pressure in an inert atmosphere such asnitrogen, initially at a temperature range of from about 125 C. to about250 C., but preferably between about 150 C. to 200 C. in the presence ofa transesterilication catalyst. During the first stage of this reaction,methyl alcohol is evolved and is continuously removed by distillation.After a reaction period of about 1 to 3 hours, the temperature of thereaction mixture is raised to from about 200 C. to about 300 C. forapproximately onehalf to three hours in order to complete the reaction,so as to form the desired polyester prepolymer and distill off anyexcess glycol.

Any known suitable transesterification or ester-interchange catalyst,for example, lithium hydride or zinc acetate, can be used to catalyzethe present transesterification reaction. Generally, thetransesterification catalyst is used in concentrations of from about0.01% to about 0.20%, based on the weight of the dialkyl terephthalateused in the initial reaction mixture.

Similarly, the preparation of polyester resins via the directesterification reaction is generally carried out with a molar ratio ofglycol, such as ethylene glycol, to a dicarboxylic acid, such asterephthalic acid, of from about 1:1 to about 15:1, but preferably fromabout 1.211 to about 2.6: 1. The direct esterification step is generallycarried out at temperatures ranging from about 180 C. to about 280 C. inthe absence of an oxygen containing atmosphere at atmospheric orelevated pressure for about two to four hours to form the desiredpolyester prepolymer. For example, the reaction may be carried out in anatmosphere of nitrogen.

Any known suitable first stage direct esterification catalytic additivemay be used in the direct esterification step of the present method. Forexample, calcium acetate or triethylamine may be used. The first stagecatalytic additives are generally used in concentrations ranging from5x10 mole to about 5x10" mole of catalytic additive per mole ofterephthalic acid present in the initial terephthalic acid-glycolreaction mixture.

The polycondensation step of the present invention is accomplished byadding a suitable orthoarsenite or orthoarsenate of a heavy metal to apolyester prepolymer or bis-Z-hydroxyethyl terephthalate and heating theblend thereof under reduced pressure within the range of from about 0.05mm. to 20 mm. of mercury while being agitated at a temperature of fromabout 260 C. to about 325 C. for from two to four hours. In accordancewith the present invention, an orthoarsenite or orthoarsenate of a heavymetal is generally employed in amounts ranging from about 0.01% to about0.2%, based on the weight of the polyester prepolymer to bepolycondensed. Usually, it has been found that from about 0.02% to about0.1% of a subject polycondensation catalyst is preferred in mostinstances. Higher or lower concentrations of an orthoarsenite ororthoarsenate of a heavy metal can also be used in the subjectpolycondenation reaction. However, when concentrations less than theabove are used, its effectiveness is generally reduced, whereas ifconcentrations greater than this are used, no further improvement in thepresent method or desired product is generally obtained.

The following examples of several preferred embodiments will furtherserve to illustrate the present invention. All parts are by weightunless otherwise indicated.

EXAMPLE I A mixture comprising 600 g. of dimethyl terephthalate, 396mls. of ethylene glycol and 0.24 g. of lithium hydride was charged intoa reaction vessel equipped with a nitrogen inlet, heating means andstirring means. The reaction mixture was agitated and heated atatmospheric pressure at 198 C. under a nitrogen blanket. The reactionmixture was held at about 198 C. for about two hours, during which timeby-product methyl alcohol was distilled off. Then the temperature of thereaction mixture was allowed to rise to 230 C. over a period of aboutone hour to distill oil any remaining by-product methyl alcohol andethylene glycol and form a polyester prepolymer. The prepolymer productwas allowed to cool under an atmosphere of nitrogen.

EXAMPLE II Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony orthoarsenate (SbAsO and placed in a reactionvessel. The reaction mixture was heated to about 280 C. under reducedpressure of about from 0.05 to about 0.1 mm. of mercury while underagitation for about three hours to bring about the polycondensation ofthe polyester prepolymer and formation of the polyester resin. Theresulting resin product had an intrinsic viscosity of 0.90, a carboxylcontent value of 20.8 (meq.kg.) and a melting point of about 262 C.

EXAMPLE III Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony orthoarsenite (SbAsO and placed in a reactionvessel. The reaction mixture was heated to about 280 C. under reducedpressure of about from 0.05 to about 0.1 mm. of mercury while underagitation for about three hours to bring about the polycondensation ofthe polyester prepolymer and formation of the polyester resin. Theresulting polyester resin product had an intrinsic viscosity of 1.01, acarboxyl content value of 13.6 (meq./kg.) and a melting point of about263 C.

EXAMPLE IV A blended mixture comprising 474 g. of terephthalic acid, 288mls. of ethylene glycol and 149 mls. of triethylamine was charged into areaction vessel equipped with a nitrogen inlet, a Dean-Starke separatingapparatus, heating means, and stirring means. The reaction mixture wasagitated and the temperature was raised to about 197 C. under a nitrogenblanket at atmospheric pressure. At about C., a Water-triethylamineazeotropic mixture started to distill off. The azeotropic mixture wascontinuously separated by means of the Dean-Starke apparatus, and thetriethylamine recovered was continuously returned to the reactionvessel. The reaction mixture became almost clear. Then, the temperaturewas allowed to rise to about 220 C. over a one hour period to form apolyester prepolymer. The prepolymer product was allowed to cool underan atmosphere of nitrogen.

EXAMPLE V Fifty grams of the prepolymer product of Example IV was mixedwith 0.02 g. of lead orthoarsenate and placed in a reaction vessel. Thereaction mixture was heated at about 280 C. under reduced pressure offrom about 0.05 to about 0.1 of mercury while under agitation for aboutthree hours to bring about the polycondensation of the polyesterprepolymer and formation of a polyester resin. The resin formed had anintrinsic viacosity of 0.74, a carboxyl content value of 11.4 (meo.-'kg.) and a melting point of about 267 C.

EXAMPLE VI Fifty grams of the prepolymer product of Example IV was mixedwith 0.02 g. of zinc orthoarsenate and placed in a reaction vessel. Thereaction mixture was heated at about 280 C. under reduced pressure ofabout 0.05 to about 0.1 mm. of mercury while under agitation for aboutthree hours to bring about the polycondensation of the polyesterprepolymer and formation of a polyester resin. The resulting polyesterresin product had an intrinsic viscosity of 0.75, a carboxyl contentvalue of 29.1 (meq./ kg.) and a melting point of about 265 C.

, EXAMPLE VII Fifty grams of the prepolymer product of Example IV wasmixed with 0.02 g. of antimony orthoarsenite (SbAsO and placed in areaction vessel. The reaction mixture was heated at about 280 C. underreduced pressure of from about 0.05 to about 0.1 mm. of mercury whileunder agitation for about three hours to bring about thepolycondensation of the polyester prepolymer and formation of apolyester resin. The resulting polyester resin product had an intrinsicviscosity of 0.81, a carboxyl content value of 6.9 (meq./kg.) and amelting point of about 263 C.

EXAMPLE VIII Fifty grams of the prepolymer product of Example IV wasmixed with 0.02 g. of antimony orthoarsenate (SbAsO and placed in areaction vessel. The reaction mixture was heated at about 280 C. underreduced pressure of from about 0.05 to about 0.1 mm. of mercury whileunder agitation for about two hours to bring about the polycondensationof the polyester prepolymer and formation of a polyester resin. Theresulting polyester resin formed had an intrinsic viscosity of 0.64, acarboxyl content value of 6.2 (meq./ kg.) and a melting point of about263 C.

EXAMPLE IX Fifty grams of the prepolymer product of Example IV was mixedwith 0.02 g. of cobaltous orthoarsenate (Co (AsO and placed in areaction vessel. The reaction mixture was heated at about 280 C. underreduced pressure of from about 0.05 to about 0.1 mm. of mercury whileunder agitation for about three hours to bring about thepolycondensation of the polyester prepolymer and formation of apolyester resin. The resulting polyester resin product had an intrinsicviscosity of 0.60, a carboxyl content value of 16 (meq./kg.) and amelting point of about 265 C.

EXAMPLE X Fifty grams of the prepolymer product of Example IV was mixedwith 0.02 g. of stannous orthoarsenate and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury while under agitation forabout three hours to bring about the polycondensation of the polyesterprepolymer and formation of a polyester resin. The resulting polyesterresin product had an intrinsic viscosity of 0.87, a carboxyl contentvalue of 15 ('rneq./kg.) and a melting point of about 263 C.

The intrinsic viscosity of the polyester resin products of the aboveexamples were measured in a 60% phenol and 50% tetrachloroethanesolution (wt/wt.) at 30 C.

The process of the present invention has been described with particularreference to polyethylene terephthalate, but it will be obvious that thesubject invention includes within its scope other polymericpolymethylene terephthalates formed from glycols of the series HO(CH),,OH, where n is 2 to 10 and terephthalic acid or esters thereof andcopolyesters containing varied amounts of other suitable dicarboxylicacids or esters thereof, such as isophthalic acid.

The polyester resins produced in the above examples were characterizedby their high molecular weights, as in dicated by their intrinsicviscosities, high melting points and low carboxyl content values,thereby making such resins particularly suitable for melt spinning intofilaments.

It will be apparent that various different embodiments can be madepracticing this invention without departing from the spirit and scopethereof, and therefore, it is not intended to be limited except asindicated in the appended claims.

We claim:

1. In a process of preparing polyethylene terephthalate resin whereindimethyl terephthalate is reacted with ethylene glycol in the presenceof an ester-interchange catalyst to form a polyester prepolymer or whereterephthalic acid is reacted with ethylene glycol in the presence of afirst stage catalytic additive to form a polyester prepolymer and wherethe resulting polyester prepolymer is polycondensed in the presence of apolycondensation catalyst, the improvement comprising adding to the saidprepolymer a catalytic amount of polycondensation catalyst consisting ofa heavy metal salt of orthoarsenious acid or orthoarsenic acid whereinthe metal component of the salt is from Groups IV-A, V-A, or VIII of thePeriodic Table (Merck Index, sixth edition) and then carrying out thepolycondensation of said prepolymer.

2. The process of claim 1 wherein the heavy metal salt is present in anamount of from about 0.01% to about 0.2%, based on the weight of thepolyester prepolymer.

3. The process of claim 1 wherein the heavy metal salt is antimonyorthoarsenite.

4. The process of claim 1, wherein the heavy metal salt is leadorthoarsenate.

5. The process of claim 1 wherein the heavy metal salt is antimonyorthoarsenate.

6. The process of claim 1 wherein the heavy metal salt is cobaltousorthoarsenate.

7. The process of claim 1 wherein the heavy metal salt is stannousorthoarsenate.

References Cited UNITED STATES PATENTS 3,068,205 12/1962 Smith 2603,389,127 6/1968 Kresse 26075 FOREIGN PATENTS 1,297,516 5/1962 France.

835,743 5/ 1960 Great Britain.

0 WILLIAM SHORT, Primary Examiner L. P. QUAST, Assistant Examiner PO-WTUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 509,099 Dated p il 28, 1970 Inventor(s) Ma Ply E Carter; JOhn A Price; andMary J. Stewart It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, lines 21 and 55, change "ter'ephthalate" t0 -terephthalic-Column 2, line 12, change o fthe" to --of the-- Column 6, line 30, after"of" insert --a-- SIGNED AND SEALED AW mm x. mm, i Edward M. mm, 1 mmam01' Pm;

Officer

